1. Considering this patient’s history and physical examination, how precisely can the neurologic lesion be localized?
Not very precisely. The sensory symptoms involving the posterior scalp region suggest a high cervical (~C2) spinal cord, dorsal root, or spinal nerve localization, but this is fairly subtle.
2. Is there evidence of peripheral nervous system involvement in this case, and, if so, what is the level(s) of the involvement? How would you characterize this peripheral nervous system involvement, if it is present?
Possibly. The bilateral distal, symmetric sensory signs and symptoms involving all four limbs raise the possibility of both a large fiber and small fiber sensory polyneuropathy.
3. Is there evidence of spinal cord involvement in this case and, if so, at what level? If spinal cord involvement is present, which specific structures are involved by the pathologic process?
Possibly. The subacute onset of bilateral, symmetric numbness and paresthesias beginning in the hands, progressing quickly to the feet, and then ascending – when coupled with very subtle upper motor neuron signs (mild weakness and mute plantar reflexes) – suggests the possibility of bilateral, symmetrical spinal cord involvement of primarily the posterior column pathways (fasciculi gracilis and cuneatus), spreading into the lateral funiculi to involve the lateral corticospinal tracts. Since distal blunting to pain and temperature is also present, the spinothalamic tracts may also be involved, or, alternatively, these findings may suggest a small fiber polyneuropathy. If spinal cord involvement is present, the cervical cord (probably as high as C2) would be the most likely site.
4. In general, what type of pathologic process do you think is involved in this case?
The findings suggest a subacute myelopathy (plus/minus a polyneuropathy). Possible causes include nutritional, toxic, inflammatory, HIV, or paraneoplastic processes. Neoplastic disease is possible, but less likely.
5. What initial diagnostic studies would you undertake at this point?
Laboratory Studies
1. Vitamin B12 level was low normal, in spite of the patient receiving monthly B12 injections
2. Methylmalonic acid, homocysteine, and copper levels were normal.
3. Autoimmune, HIV, and other inflammatory studies were normal.
4. CSF studies were normal, including multiple sclerosis studies.
5. EMG and nerve conduction studies (NCS) were normal and did not document a peripheral neuropathy.
6. Bilateral median nerve somatic sensory evoked potentials (SSEP) showed delayed central conduction velocities, indicating dysfunction of central large fiber sensory pathways (i.e., the posterior column-medial lemniscus pathways).
6. This patient’s illness represents a classic neurologic syndrome. What is the name of this syndrome, and what is its etiology?
Subacute combined degeneration (SCD). This is usually due to vitamin B12 deficiency, which can result from many causes.
7. What additional diagnostic procedures would you undertake at this point?
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